Organoaluminum complexes have been used in the electrolytic deposition of aluminum for quite some time (Ph.D. Thesis by H. Lehmkuhl, T H Aachen 1954, DE-PS 10 47 450, K. Ziegler, H. Lehmkuhl, Z. Anorg. Allg. Chemie 283, 414 (1956); DE-PS 10 56 377; H. Lehmkuhl, Chem. 1 ng. Tech. 36, 616 (1964); EP-A-0 084 816; H. Lehmkuhl, K. Mehler and U. Landau in Adv. in Electrochem. Science and Engineering (Ed. H. Gerischer, C. W. Tobias) Vol. 3, Weinheim 1994).
There has been rapidly increasing interest in electrolytic coating of metallic materials with aluminum or aluminum-magnesium because such coatings have excellent corrosion protection and are ecologically safe. Therefore, electroplating using organoaluminum electrolytes operating at moderately elevated temperatures of between 60 and 150° C. and in closed systems is of major technical importance.
The PCT/EP application WO 00/32847 describes organoaluminum electrolytes suitable for electrochemical deposition of aluminum-magnesium alloys in technical applications as well. Such electrolytes contain alkali tetraalkylaluminum components, particularly K[AlEt4], and in a preferred embodiment in mixture with Na[AlEt4], the molar ratio of sodium/potassium component being less than 1:3. These electrolytes also contain trialkylaluminum, preferably AlEt3, as well as toluene or liquid xylene as preferred solvent.